1. Field of the Invention
This invention relates to pumps (hereinafter referred to as being of the kind specified) each such pump comprising a body having at least one pumping chamber communicating at opposite ends and respectively with a pump inlet and a pump outlet, an actuator in the pumping chamber reciprocable longitudinally thereof by drive means and having a relatively rigid main central portion and a peripherally extending sealing ring retained in a clearance space and in non-sliding fluid-tight engagement between the central portion and a lateral wall of the pumping chamber, valve means controlling the flow of fluid through the pumping chamber from the inlet to the outlet, and fluid inductance means and fluid capacitance means operative between the pump inlet and outlet for controlling the operational characteristic of the pump.
2. Description of the Prior Art
A pump of the kind specified was disclosed and claimed in our prior U.S. Pat. No. 3,307,492. The practical embodiments disclosed were intended for use in pumping water, possibly with suspended solids, for drainage purposes of the sites of building or civil engineering work and for such applications and others to which such pumps were intended to be applied the outlet of the pump would be permanently open. To assist priming, the valve means provided included not only a one-way valve mounted on the actuator itself (the actuator valve means) but also further one-way valves situated in the flow path of the liquid through the pump for permitting only flow in a direction from the inlet to the outlet of the pump and situated upstream and downstream of the actuator. In particular the one-way valve provided downstream of the actuator was positioned between the actuator and the fluid capacitance (referred to in our prior patent aforesaid as a pressure absorbing and restoring means).
Whilst the configurations, i.e. the general arrangement of actuator valve means and fluid capacitance and inductance (the last mentioned being referred to in our prior patent aforesaid as a slug duct section), are eminently suitable for pumps such as those intended to be used as aforesaid at civil engineering or building sites or elsewhere in cases where a permanently open pump outlet is called for or is acceptable, they are not suitable for certain other applications.
In particular, in many forms of fluid handling plant in which a pump is required to be installed, the delivery of fluid from the outlet of the pump may be controlled by a stop valve situated at or downstream of the pump outlet and which, when closed manually or otherwise, prevents or severely restricts the delivery of the fluid. Similar or analogous conditions of operation may arise in other circumstances.
In such circumstances the practical embodiments of the pump disclosed in our aforementioned prior patent would give rise to the problem that there would be an excessive rise of pressure in the pumping chamber downstream of the actuator and damage to the pump could occur in consequence of this either by exceeding the stress limit for the pumping chamber itself or for components of the drive means or actuator. It would not be possible for the excessive pressure rise to be relieved or reduced by flow of fluid internally of the pump between one and another of a plurality of pumping chambers because communication between the chambers would, under conditions of shut-down, be blocked or disabled by the one-way valves situated at the outlet of the pumping chambers. Further, the fluid capacitance means, if contained in, or partly in, the chambers, would not be effectively or fully effective to relieve the adverse conditions.
Further, the conventional solution of providing a separate relief valve would entail quite severe economic penalties since relief valves which perform reliably and satisfactorily under a wide variety of conditions of operation involve high manufacturing costs, possibly approaching those of the pump itself.